Hydrogeological Impact Assessment of Tunnel Excavation Using the TOUGH3–FLAC3D Coupled Modeling Approach

Abstract

Tunnel excavation in complex geological settings often induces groundwater inflow, which poses substantial engineering and environmental challenges. Excessive inflow can cause flooding, collapse, and structural instability, leading to delays and increased construction costs. This study employs a coupled TOUGH3–FLAC3D model to investigate the hydro-mechanical interactions between groundwater flow and rock deformation during tunnel excavation. The three-dimensional hydrogeological conceptual model was established based on field geological data and digital terrain to simulate groundwater responses. Simulation results indicate that excavation in the Kangkou Formation may induce a groundwater head decline of 7–10 m near the tunnel and increase local inflow rates up to 7.7 L/min when intersecting the Waiao Fault. The results reveal that under bare rock conditions, tunnel inflow has a negligible effect on reservoir recharge. However, when the tunnel intersects high-permeability fault zones, mitigation measures such as grouting or water-blocking tunnel designs should be implemented to reduce potential impacts on the groundwater system.